The dyestuff of the lithospermum root is extracted from a root of lithospermum [botanical name: Lithospermum erythrorhizon Siebold et Zuccarini (Lithospermum officinale linne var. erythrorhizon Maimowicz)(Borraginacease)], and this dyestuff has been long used from of old as the valuable dye for obtaining a dyeing of a purple color regarded as a "noblest color" in Japan. It is known that this dyestuff is not subject to discoloration and has a good heat resistance, oxidation resistance and light resistance, and that this dyestuff of the lithospermum root has a high safety and is utilized as the coloring material for foods and cosmetics. Practically, at present, this dyestuff is used in the field of cosmetics as a dyestuff applicable to mucosa, i.e., as coloring materials such as lipsticks and eye shadows, but a process for preparing a black coloring material from the dyestuff of the lithospermum root has not been known.
As the conventional black coloring material, there can be mentioned inorganic pigments such as carbon black and black iron oxide, organic pigments such as Aniline Black, tar dyestuffs such as Black dyestuff 401, and various dyes.
These pigments and dyes, however, are not completely satisfactory in safety, allowable application range or lightness (blackness) expected as a black coloring material.
The conventional black-dyeing dyes used for obtaining a finely divided black coloring material from a natural or synthetic polymer as the base or a black fiber have problems in that a heavy metal such as chromium must be used for the dyeing operation and a subsidiary material such as a surface active agent must be used, and some of dyeing methods using these dyes damage the dyed products. In general, an intended black coloring material or black fiber cannot be obtained by a simple dyeing method.
As the carbon black, there can be mentioned furnace black obtained by a continuous incomplete combustion of a natural gas or a petroleum or coal type heavy hydrocarbon oil in a reaction furnace and channel black obtained by burning a natural gas or hydrocarbon gas as a low flame, bringing the low flame into contact with the bottom surface of a channel steel, and collecting carbon formed by a continuous flame decomposition. It is reported that furnace black contains benzpyrene, which is a carcinogenic substance, and in Japan only the use of channel black is allowed in the field of cosmetics, and in the United States, the use of both carbon blacks is inhibited. Accordingly, carbon black cannot be regarded as a safe black coloring material.
Black iron oxide (tri-iron tetroxide, FeO.Fe.sub.2 O.sub.3) is not a black coloring material showing a black color with a satisfactorily low lightness.
From the viewpoint of safety, the use of organic pigments such as Aniline Black is not allowed for medicines and cosmetics.
Also, tar type dyestuffs involve a risk of toxicity on a human body, and the applicable range is strictly restricted. For example, Black dyestuff 401 formed by subjecting Naphthol Blue Black, which is a tar type dyestuff, to a lake-forming reaction with aluminum sulfate cannot be used for a product to be applied onto a mucous membrane portion, and use of this dyestuff is greatly restricted. Moreover, in general, tar type dyestuffs have inferior fastness characteristics to inorganic black coloring materials such as black iron oxide, and tar type dyestuffs have problems in that they are slightly eluted into water even under neutral conditions.
As the black-dyeing dye conventionally used for obtaining a finely divided black coloring material from a natural or synthetic polymer as the base or a black fiber, there can be mentioned Acid Fast Black VLG (color index and number: C.I. Acid Black 25; dyes and pigments will be indicated in the same manner hereinafter), Acid Black WA (C.I. Acid Black 52), Chrome Black P2B (C.I. Mordant Black 7) and Chrome Black T (C.I. Mordant Black 11), which have been used for dyeing such substrates as wool, silk and nylon to a black color, and Reactive Black B (C.I. Reactive Black 5) which has been used for dyeing such substrates as cotton and rayon to a black color. Acid Fast Black VLG is a milling type acid dye, for which an addition of a nonionic or amphoteric surface active agent as a subsidiary agent is necessary, and since this dye has a relatively high molecular weight, the dye is suitable for dyeing a coarse fiber but has a poor compatibility with a finely divided substrate. Acid Black WA is a 1:1 type chromium complex salt dye and when this dye is used, single-bath dyeing is possible. Nevertheless, since the dyeing operation is carried out at a pH value of about 2, wool or the like is easily damaged, and therefore, this dye is now used only for a limited number of specific articles. Each of Chrome Black P2B and Chrome Black T is a chromium dye, and when these dyes are used, a dyeing process is adopted in which a chromium complex is formed on a fiber or other substrate to be dyed by using a dichromate. These chromium dyes are disadvantageous in that the use of chromium, a heavy metal, cannot be avoided.
Reactive Black B is a reactive dyestuff, and this dye has a problem in that, as in the case of other reactive dyestuffs, a long time and a large amount of energy are necessary for the washing operation conducted after the dyeing.